User:Quercus solaris/Dislocated heart, dislocated heartbeat

It is an accident of idiom that ectopia cordis and cardiac ectopy are not synonymous. Most such Latin/English pairs are indeed synonymous, as well they ought to be and usually can hardly help but be. For example, the bulbus cordis is the bulb of the heart, and they could hardly be different things even if you wanted them to be. That is, the words could hardly refer to different ideas even if you wanted them to do so. But ectopia cordis is abnormal location of the heart, whereas cardiac ectopy is, in its usual sense, abnormal location of the heartbeat (that is, its impulse/generation).

How do idiomatic snares such as this one happen? Some thoughts:
 * 1) Metonymy. In natural language it was perhaps inevitable that cardiac would end up referring both to the heart and to the heartbeat, with the sense disambiguation relying on context. So obvious, in a fail-was-inevitable kind of way. Not really that complicated, and not hard to understand—for a human at least. But of course jokes like this are why machines have been having such a hard time learning to speak human languages. Oh well. Give it a few more decades. Maybe by then you'll be having a natural discussion with a machine about how silly it all is. And you, at least, can laugh. A few more decades after that, maybe you both will laugh.
 * 2) Compare another instance in this neighborhood, which is medical history versus history of medicine—the one refers by convention to a person's history, the other to a field's history
 * 3)  Reservation of particular inflections for particular senses. This is another natural process that happens over time.
 * 4) An example is urinary diversion versus urine diversion.
 * 5) The term urinary diversion (adjective inflection + noun) by convention via decades of use refers to the diversion of urine to alternative routes within the body, i.e., a surgical therapy in health care, whereas urine diversion is a collocation coined much later that refers to the diversion of urine to alternative routes in the plumbing and thus subsequently in the ecosan system, e.g., by bypassing the sewer and water treatment pathways and diverting to fertilizer, pharmaceutical, or other chemical industry manufacture.
 * 6) This pair is thus a member of the class of "cases where the noun adjunct is not interchangeable with the adjectival form"—a topic discussed at noun adjunct.
 * 7) Another example is optic disc versus optical disc; neither is an idiomatic replacement for the other, even though their interchange by a nonnative speaker would not raise any eyebrows, or any questions about intended meaning.
 * 8) Another example is reticulocytes versus reticular cells, quod vide.